Increased global demand and consumption of easily accessible petroleum and natural fossil fuels continues to be unpredictable in future prices and put a constant pressure on economies, politics, and importantly, the environment. These pressing issues have led to a growing need for alternative, renewable, and sustainable energy sources and additional developments in production of alternative fuels.
Currently, the largest volume of renewable fuel sources or biofuels is derived from agricultural feedstocks including plant-based sugars and oils (i.e. carbohydrates and acylglycerols, respectively) and other derivatives. However, reliance on edible crop-based fuels is not a long-term energy solution since premium farmland, abundance of water, and energy are in limited supply. Therefore, it is beneficial to seek out additional sources for biofuels and efficient methods of production.
In recent years, potential biofuel sources such as algae have shown to be promising alternatives to crop-based biofuels. Advances in cultivation, processing, and production have demonstrated not only the feasibility of using algal sources in terms of cost, labor, and time, but also the potential value in parallel production of commercially useful co-products.
Algae can produce 10 to 100 times as much mass as terrestrial plants in a year. Algae also produce oils (lipids) and starches that may be converted into biofuels. Algae useful for biofuel production include algae known as microalgae, consisting of small, often unicellular, types. These algae can grow almost anywhere, though most are commonly found at latitudes between 40 N and 40 S. With more than 100,000 known species of diatoms (a type of algae), 40,000 known species of green plant-like algae, and smaller numbers of other algae species, algae will grow rapidly in nearly any environment, with almost any kind of water, including marginal areas with limited or poor quality water.
While the cost of petroleum has increased dramatically in recent years, critics remain who contend that nonetheless algal biofuels will prove too costly to manufacture on a larger scale, and that algae productivities do not surpass those of irrigated crops and cultivating, harvesting, and processing microalgae is simply too expensive. Adding the production of both supplementary biofuels and valuable co-products can make energy production using algae commercially viable and a key reason to further explore algae as a biofuel source.
The most notable product yielded from algal biofuel production is biodiesel in the form of long-chain alkyl esters and more specifically, fatty acid methyl esters (FAMEs). However, another unique and promising class of algal compounds known as long-chain alkenones (e.g. alkenones) are naturally biosynthesized by certain species of algae, namely members of the Isochrysis, Emiliania, and the Gephyrocapsa families, in parallel to compounds required for biodiesel production. Alkenones may be converted to smaller hydrocarbon fragments in the range of jet fuel and kerosene through a separate processing method than utilized for biodiesel/FAME synthesis. Thus, jet fuel-range biofuels may be produced in parallel with biodiesel from a single batch of algae, adding another level of commercial value.
Additionally, from this single batch of algae, it is possible to simultaneously isolate other valuable co-products such as fucoxanthin, astaxanthin, beta-carotene, and other carotenoids. Fucoxanthin, in particular, has been reported for health benefits as an antioxidant, anti-inflammatory, anti-cancer chemical with industrial uses as well. Therefore, there is an unmet need and desire to use algae not only as a diversified source of biodiesel which does not rely on food resources, but as an economically viable source of biodiesel, biofuel, and additional desirable co-products.